Filter plate for a coating head

ABSTRACT

IN A NONCONTACTING COATING HEAD IN WHICH DROPS OF COATING ARE EJECTED FROM VERY SMALL ORIFICES IN AN ORIFICE PLATE TOWARD A WEB OR OTHER ARTICLE BEING COATED, A FILTER PLATE HAVING PERFORATIONS THEREIN NO LARGER THAN THE ORIFICES IS MOUNTED DIRECTLY IN THE COATING HEAD JUST UPSTREAM OF THE ORIFICE PLATE TO REMOVE FROM THE COATING MATERIAL ANY PARTICLES OF A SIZE SUFFICIENT TO CLOG THE ORIFICES. THE TOTAL OPEN AREA OF THE PERFORATIONS IS GREATER THAN THE TOTAL OPEN AREA OF THE ORIFICES SO THAT AN APPRECIABLE NUMBER OF PERFORATIONS CAN BE BLOCKED BY A FOREIGN PARTICLES WITHOUT SERIOUSLY AFFECTING OPERATION OF THE COATING HEAD.

- Sept. 21,1971 ,1, p v s 3,606,973

FILTER PLATE FOR A 'COATING HEAD Filed Nov. 1'7, 1969 FIG-2 2o [23 INVENTOR GERALD T. DAVIS A TTORNE Y5 United States Patent 3,606,973 FILTER PLATE FOR A COATING HEAD Gerald T. Davis, Chillicothe, Ohio, assignor to The Mead Corporation, Dayton, Ohio Filed Nov. 17, 1969, Ser. No. 877,251 Int. Cl. B05b 5/00 US. Cl. 23915 8 Claims ABSTRACT OF THE DISCLOSURE In a noncontacting coating head in which drops of coating are ejected from very small orifices in an orifice plate toward a web or other article being coated, a filter plate having perforations therein no larger than the orifices is mounted directly in the coating head just upstream of the orifice plate to remove from the coating material any particles of a size sufiicient to clog the orifices. The total open area of the perforations is greater than the total open area of the orifices so that an appreciable number of perforations can be blocked by foreign particles without seriously affecting operation of the coating head.

CROSS REFERENCE TO RELATED APPLICATIONS Image Construction System Using Multiple Arrays of Drop Generators, Ser. No. 768,790, filed Oct. 18, 1968 now Pat. No. 3,560,641; Method of Assembling a Coating Head and Sub-Assembly Thereof Ser. No. 877,255, filed Nov. 17, 196 9; and Inlet Plate for Coating Head, Ser. No. 877,256, filed Nov. 17, 1969.

BACKGROUND OF THE INVENTION The above noted related application Ser. No. 768,790 discloses a noncontacting coating system in which a plurality of drops are ejected from a series of small orifices toward a moving web or other article to be provided with .a patterned coating, as in printing, with selected drops being charged as they issue from the orifices so that when they subsequently pass through an electrostatic deflecting field established downstream of the charging means, they will be deflected from their normal trajectory. In this way, some of the drops will follow one path into a catcher while the remaining drops are deposited upon the web in the desired pattern of coating.

The dimensions of the various components of the system are relatively small. For example, the diameter of the orifices through which the coating drops are ejected may be on the order of .0015 inch. Obviously, such small openings can be readily clogged by foreign materials of what would oridinarily be considered an insignificant size and lead to malfunctioning of the coating apparatus.

Because of these considerations, any particles of a size sufiicient to clog the orifices must be removed from the system before they reach the orifice plate. However, because the materials which would clog the orifices may be extremely small, the possible sources of such contaminants are greatly multiplied. Therefore, merely filtering the coating material before it is pumped to the coating head may not be sufiicient to prevent malfunctioning through clogging since contaminants may be injected into the system between a filter, in a conduit, for example, and the coating head.

SUMMARY OF THE INVENTION A plate member having a multiplicity of perforations, each of which is no larger than the orifices through which the coating drops are ejected, is positioned immediately upstream of the orifice plate and thereby removes from the coating material any particles of a size large enough to clog the orifices in the orifice plate. Since the orifices are the smallest diameter opening in any of the compo- 3,606,973 Patented Sept. 21, 1971 BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an exploded perspective view showing, somewhat schematically, the various components of the laminated coating head; and

FIG. 2 is a plan view of a filter plate constructed in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As seen in FIG. 1 of the drawings, a typical laminated coating head may comprise a manifold 10 having a chamber 11 opening outwardly, as at 12, and a conduit 13 for delivering coating material to the chamber 11. The filter plate 20 may be positioned immediately beneath the manifold 10 and have gaskets 21 and 22 positioned on either side thereof to prevent leakage around the filter plate when the components are assembled. The filter plate 20 as seen in more detail in FIG. 2, has a central portion 23 thereof provided with a multiplicity of small perforations 24. The perforated central portion of the plate 20 can be conveniently fabricated by conventional photofabrication techniques such as etching or electroplating and an arrangement of the perforations in a array with a total of approximately 41,000 perforations has proven satisfactory.

An inlet plate 30 having a slot 31 formed longitudinally thereof and a series of passages 32 extending from the slot to the lower surface of the inlet plate is positioned immediately beneath the filter plate 20 with the slot 31 substantially aligned with the perforated central portion of the filter plate 20.

Immediately beneath the inlet plate 30 is an orifice plate 40 having a series of orifices 41 formed therein. Coating material pumped into the coating head through the conduit 13 is ejected through the orifices 41 in fine filaments which break into the drops of coating material which are projected onto the article being coated. Obviously, the orifice plate is positioned with respect to the inlet plate such that the orifices 41 are concentrically aligned with respect to the passages 32.

A spacer plate 50 is mounted beneath the orifice plate 40 and serves to space the charge ring plate 51 the proper distance from the orifice plate to impart a charge on the drops of coating material just before they break from the filament of coating being ejected through the orifices 41.

The charge ring plate 51 has a series of charge rings 52 connected through leads 53 and connectors 54 to a source of power 55; whereby an electric charge may be imparted to drops of coating material as they are ejected from the orifices 41. The charge ring plate, including its associated charge rings and leads, may be conveniently constructed by conventional printed circuit techniques, although it will be appreciated that the degree of precision required will be somewhat greater than is often demanded in the printed circuitry art.

A clamp plate 56 is positioned adjacent the charge ring plate 51 and a series of bolts, not shown, pass downwardly through all of the components of the laminated coating head and are threadedly received in the clamp plate to secure the components together in laminar relationship.

A pair of electrodes 57 are positioned downstream of the charge ring plate and all drops, whether charged or uncharged pass through the electrostatic field set up by the electrodes 57 and are accordingly deflected or not deflected depending upon whether or not they have received a charge as they pass through the charge ring plate. A catcher 58 then catches those drops of coating material which it is desired to prevent being deposited on the article being coated, all as described in application Ser. No. 768,790.

As noted above, the openings through all of the components of the laminated coating head are relatively small. For example, the orifices 41, which are smaller than any of the openings through any of the other components of the coating head, may be on the order of .0015 inch in diameter. Therefore, by placing the filter plate 20 having a central portion 23 provided with a series of perforations 24 therethrough of a diameter no greater than that of the orifices 41, any particles of a size which might clog any of the openings in the coating head components are deposited out of the coating material on the plate 20.

While a filter plate 20 having openings 24 therethrough the same size as the diameter of the orifices would effectively remove any spherical particles which might clog the orifices from the coating, it will be appreciated that an elongated particle with a diameter less than the orifices might pass through a filter plate having perforations of the same diameter and then by turning before it reached the filter plate, staple across an orifice and either alone, or in conjunction with other smaller particles effectively block the orifice. Therefore, the perforations through the filter plate have been formed approximately .0005 inch in diameter and this has been found effective to remove elongated as well as spherical particles which might cause malfunction of the system.

As noted above, because of the relatively small size of the particles which might block the orifices, it is desirable to place the filter plate as close as physically possible to the orifice plate to diminish the number of possible sources of contaminants. Theoretically of course, this would mean positioning the filter plate in contiguous relationship with the orifice plate. It will be appreciated however, that the number of openings in the filter plate through which the coating might pass to reach an individ ual orifice would be decreased considerably. Additionally, passage of the coating material through the filter plate may generate fine scale turbulence which could cause nonuniformity in the drops of coating being ejected from the orifice plate. Therefore, the filter plate is positioned a short distance upstream of the orifice plate by means of the inlet plate 30. Thus, any turbulence generated in the coating material by its passage through the perforations 24 decays as it passes through the slot 31 and passages 32 in the inlet plate. Additionally, spacing of the filter plate from the orifice plate permits, in effect, several of the perforations 24 to communicate with each of the orifices 41. This may be particularly important where particles screened out by the filter plate 20 block several of the openings 24, thereby necessitating increased flow through the unblocked perforations.

From the above it will be apparent that the present invention provides means for preventing malfunctioning of the coating apparatus through clogging of any of the openings through any of the components thereof through the introduction of foreign materials to the coating.

While the form of apparatus herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the invention.

What is claimed is:

1. In noncontacting coating apparatus including a coating material manifold, an orifice plate having a series of orifices therethrough, a series of charge rings positioned downstream of and concentric with said orifices for selectively imparting an electric charge on coating material ejected through said orifices, means positioned downstream of said charge rings for establishing an electrostatic field and means for selectively catching drops of coating material after they have passed through said electrostatic field, the improvement comprising:

(a) a filter plate interposed between said manifiold and said orifice plate, e (b) said filter plate having a series of perforations formed therein, (c) said perforations being no greater in dimension than said orifices.

2. The improvement of claim 1 wherein:

(a) the total area of said perforations is greater than the total area of said orifices.

3. The improvement of claim l wherein:

(a) said filter plate is spaced from said orifice plate.

4. The improvement of claim 2 wherein:

(a) at least the major portion of said perforations are approximately 0.0005 inch in diameter.

5. The improvements of claim 1 wherein:

(a) said perforations are grouped in a central portion of said plate.

6. The improvement of claim 1 wherein:

(a) said perforations are arranged in a 90 array.

7. The improvement of claim 1 wherein:

(a) there are approximately 41,000 perforations in said filter plate.

8. For use in a noncontacting coating apparatus including means for supplying coating material to a series of orifices formed in an orifice plate, means for selectively charging coating material ejected through said orifices, means for establishing an electrostatic deflection field beneath said charge means and means for catching selected portions of said coating material passing through said deflection field, the improvement comprising:

(a) an elongated, substantially rectangular filter plate positioned in said apparatus 'upstream of said orifices,

(b) said filter plate having a series of closely spaced perforations grouped in a central portion thereof,

(0) said filter plate being approximately 0.001 inch thick, and having approximately 41,000 of said perforations arranged in a 90 array with each of said perforations being no greater than 0.0015 inch in diameter.

References Cited UNITED STATES PATENTS LLOYD L. KING, Primary Examiner US. Cl. X.R. 239-557; 346 

